The invention relates to tire deflation detection systems, and more particularly to methods of improving the accuracy of tire deflation detection systems.
Tire deflation detection systems are well-known for determining when the air pressure in a vehicle""s tire has fallen below a predetermined point. There are numerous methods available to detect tire deflation, most of which use the wheel speed sensors that have been placed at each wheel in conjunction with anti-lock brake systems (ABS). The wheel speed sensors collect wheel speed data that can be processed by any number of algorithms designed to determine when one of the tires on the vehicle has become deflated. When a deflated tire is detected, a warning is issued to the driver.
As deflation detection systems have developed, they have become more and more accurate under a wider variety of driving conditions. Great efforts have been made to refine and improve the algorithms to increase the extent of their applicability. While the occurrence of false warnings is going down, the design limitations in the detection algorithms make it impossible to account for every possible driving condition, and therefore impossible to completely eliminate false warnings. False warnings, or the indication of a deflated tire when no tire is actually deflated, are annoying and frustrating to drivers. When a false warning occurs, the driver will check the tire pressure, determine that no deflation exists, and decide that the system has issued a false warning. If this occurrence is allowed to repeat, the driver may eventually ignore all future warnings, anticipating the needless inconvenience due to the perceived random behavior of the system. Eventually the driver could ignore a proper warning. Disregard for a proper warning could have potentially dangerous consequences.
Drivers are often unaware of the technology used in these deflation detection systems and have little or no understanding of how the systems operate. The drivers do not appreciate the engineering trade-offs built into the detection algorithms. These trade-offs define the particular strengths and weaknesses of the detection algorithm. Most false warnings occur for a reason, but those reasons are not usually evident to the driver.
For example, most deflation detection systems include a calibration portion of the algorithm that runs prior to the actual detection portion of the algorithm. During calibration, the system is xe2x80x9clearningxe2x80x9d the baseline for the variables that impact the measured wheel speeds. The calibration portion of the algorithm characterizes the tires with respect to inflation pressure, specific tire model, and manufacturing variations. These variables are influenced by the driving conditions experienced during calibration. Specifically, the road conditions and the amount of vehicle maneuvering during calibration will influence the calibration values obtained. The calibration process typically occurs after the system is reset, indicating that the driver believes that all of the tires are normally inflated.
Once the calibration process is completed, the calibration values are stored and used as benchmarks or as correction factors. From that time on, the wheel speeds are evaluated against this benchmark, or the correction factors are applied to the current wheel speeds. If the usage of the vehicle or the driving conditions remain substantially constant between the calibration process and the actual deflation detection process, the deflation detection system should operate properly.
If, however, the usage of the vehicle or the driving conditions change between the calibration process and the actual deflation detection process, the system will be susceptible to issuing false warnings. Examples of some of the scenarios that would tend to trigger false warnings are non-uniform loading of the vehicle, usage of non-OEM (Original Equipment Manufacturer) or non-recommended tires having different characteristics than OEM tires, mixed tire configurations (i.e., snow tires on one axle and summer tires on the other axle), usage of tire chains, and sun loading on one side of the vehicle.
Extreme driving conditions, such as high speed driving, driving under high accelerative forces (i.e., uphill driving), and severe vehicle maneuvering also pose problems for most deflation detection systems. In the past, detection algorithms have simply filtered out data collected under extreme driving conditions, but for newer systems that attempt to account for these conditions, false warnings can still occur.
Prior art deflation detection systems are open-loop, meaning that there is no feedback available to determine whether a warning was issued improperly. Additionally in open-loop systems, there is no way of preventing a previously issued improper warning from being issued again in the future. Once the prior art systems are reset, the open-loop programming of the algorithms make them prone to making the same errors and misjudgments again and again.
The present invention mitigates the annoyance of repeated erroneous warnings by providing a method of using driver feedback to determine whether a warning was properly issued. If it is determined that the warning was improper, adjustments are made to the algorithm to help prevent the same improper warning from issuing again in the future. The method of the present invention includes a feedback loop that can be designed into virtually any new deflation detection system or can be added on to virtually any existing system. By making the system a closed-loop system, it is possible to greatly reduce or eliminate the repeated occurrence of false warnings.
With the current invention, the decision to issue a warning may be incorrect once, but after that incident, the deflation detection algorithm will have feedback that the previous judgment was incorrect Future detection decisions can be modified to avoid repeating the false warning under similar circumstances. The exact action to take will vary depending on the deflation detection algorithm, but in many cases, the sensitivity of the detection algorithm can be reduced by modifying either the deflation detection threshold value or the signal values being compared to the threshold value.
The preferred embodiment of the present invention utilizes an inferred feedback component to determine whether a warning was properly or improperly issued. The preferred embodiment compares pre-warning signals, collected prior to the issuance of the warning, with post-warning signals, collected after the system has been reset, to determine whether the warning was proper. The comparison sheds light on whether corrective action was actually taken by the driver, or whether the driver checked the tires, found no actual deflation, and pushed the reset button to reset the system. In the case where the driver found no actual deflation, the present invention assumes that the warning was erroneous (due to some atypical usage of the vehicle not accounted for in the algorithm) and then makes a correction to the algorithm to prevent the repeated erroneous warning in the future.
The inferred feedback component also attempts to determine whether the driver actually checked for a deflation after a warning was issued. Modern vehicles are equipped with numerous features that can be used by the present invention to indirectly determine whether the driver acknowledged the issued warning and took action to check the tires. Determining whether the vehicle came to a complete stop, whether the transmission was shifted into park, whether the parking brake was set, whether the ignition was turned off, and whether the driver""s door was opened and closed are just a few of the determinations that can be useful for the present invention.
In an alternative embodiment, the invention can utilize a direct feedback component, which relies on direct driver input to determine whether a warning was properly issued. In this embodiment, the driver must directly communicate with the tire deflation detection system by selecting the appropriate button or signal device to let the detection system know if the warning was proper or erroneous.